[youtube https://www.youtube.com/watch?v=8o8E0yzmE3E] I set up a small magnetic dry-erase board. I would write a word using lowercase print letters. Alexander has some uppercase wooden magnet letters, and he would place the appropriate letter on the dry-erase board.
Certain lowercase letters are a challenge. A lowercase L looks like an uppercase i (and the number 1). Lowercase d, b, q, and p are similar to each other, so those are often confused. And finally, lowercase f and t are similar as well, and he sometimes confuses them. He's able to get the word correct about 80% of the time, and we're slowly working on the rest of the letters.
In Montessori (and in general, I believe) it's recommended to start by introducing lowercase cursive letters! I didn't know that, so we started with print. We're moving backwards, but hopefully (and I'm sure) he'll catch up in no time.